The present invention relates to a cooling water supply system for cooling a semiconductor integrated circuit. More particularly, the present invention is concerned with a temperature control system which is suitable for use in cooling a large-scale computer and effective in suppressing dewing on cooling pipes and LSI substrates.
In general, a large-scale computer incorporates a number of LSIs each of which generate heat. To cool these LSIs, it has been a common measure to circulate cooling water in contact with the reverse sides of the LSI substrates so as to directly cool the LSIs. The cooling water which has been heated as a result of cooling of the LSIs is cooled by a refrigeration cooling system which is composed of a compressor, a condenser, an evaporator and an expansion valve through which a refrigerant such as freon is circulated while making phase changes. Such a known cooling system is exemplarily shown in FIG. 18. The cooling water for cooling LSIs is circulated through a cooling line 3 by a pump 4 and is cooled by a first heat exchanger 7 which is the evaporator of a refrigeration cooling system. The refrigeration cooling system has a compressor 8, a second heat exchanger (condenser) 12, an expansion valve 14 and the above-mentioned first heat exchanger (evaporator) 7 which are connected in a closed loop of a refrigerant line 6 through which a refrigerant such as freon flows. The refrigerant frees heat in the condenser 12 through which an external cooling water is supplied to carry the heat away from the condenser.
In the above-described temperature control system, it is often experienced that the temperature of water for cooling LSIs is undesirably deviated from a predetermined command temperature due to various reasons such as (1) mismatching between the rate of generation of heat from the LSIs and the cooling power of the refrigeration cooling system which is determined by the power of the motor for driving the compressor of the refrigeration cooling system, and (2) a fluctuation of the temperature of the cooling water circulated through the condenser. More specifically, compressor motors of refrigeration cooling system now available are standardized and have respective rated capacities. Such motors are used in, for example, in Japan in which commercial electrical power is supplied at 50 Hz or 60 Hz, so that the cooling capacities of the refrigeration cooling systems are substantially fixed. It is not easy to obtain a matching between the cooling capacity which is fixed and the varying cooling load, i.e., the heat generation from LSIs. Referring now to the fluctuation of the cooling water temperature, the heat carried by the cooling water is radiated to the ambient air from a cooling tower through which the cooling water is circulated. The rate of heat radiation to the ambient air, however, varies depending on the temperature of the ambient air. This causes a change in the temperature of the cooling water circulated through the condenser of the refrigeration cooling system resulting in the cooling power being changed.
Control of the temperature of the cooling water for cooling LSIs is a critical requirement because a too high cooling water temperature allows LSIs to be overheated resulting in malfunctioning of the electronic circuit incorporating the LSIs, while a too low cooling water temperature undesirably allows dewing on the cooling water pipes or on the LSI substrates particularly when the humidity of the ambient air is high, causing an impediment in the safe functioning of the electronic circuit. From the view point of stable and reliable operation of LSIs, therefore, it is highly desirable that the cooling water temperature is maintained within a small range of temperature offset from a command temperature.
One of the methods commonly used for controlling the cooling water temperature in conformity with the command cooling water temperature is to repeatedly start and stop the compressor of the refrigeration cooling system. More specifically, when the temperature of the cooling water decreases below the command temperature for a reason such as that described before, the compressor of the refrigeration cooling system is stopped to allow the temperature of the cooling water or the LSIs to rise and approach the command temperature. When the cooling water temperature exceeds the command temperature during suspension of the compressor, the compressor is started again to cool the cooling water to lower the cooling water temperature to the level of the command temperature. When this cooling water temperature control method is used, the repeated start and stop of the compressor tend to cause an abrupt temperature change of the LSIs and, in addition, the amount of offset of the cooling water temperature undesirably from the command temperature increases. In order to overcome such problems, it is necessary that the quantity of the cooling water in the water cooling system be increased so as to minimize the influence of the repeated start and stop of the compressor. It will be understood that the greater quantity of cooling water provides a greater heat capacity so that the rate of change in the cooling water due to start a starting and stopping of the compressor is reduced to suppress the change in the temperature of the cooling water. To realize such a measure, one of the conventional system employs a water reservoir or tank 20 in the closed loop of the cooling water system shown in FIG. 18. The cooling system operates with the water tank 20 substantially filled with cooling water so that the quantity of water possessed by the cooling water system is increased so as to avoid any abrupt change in the LSI cooling water temperature attributable to the change in the cooling power caused by repeated start and stop of the compressor.
The other problem, i.e., dewing on the LSI substrates, is liable to occur also when a large-scale computer is started.
For instance, it is assumed here that operation of a large-scale computer with number of LSIs has been suspended long, with an air heating system of the computer room also having been kept inoperative. If the air heating system of the computer room is started simultaneously with the start of the computer, the temperature of the ambient air in the computer room rises while the cooling water temperature is still low due to the large heat capacity of the water. Consequently, the temperature of the cooling water pipes and the LSI substrates may decrease to a temperature below the dewing point which is determined by the temperature and humidity of the air in the room. In such a case, the water content of the air is condensed to form dews on the cooling water pipes and the LSI substrates. In order to obviate this problem, it is necessary to rise the temperature of the LSI cooling water to a comparatively high level before the air temperature is raised by air heating system, when a large-scale computer is started after a long suspension of operation, i.e., from a state in which the cooling water has been lowered to the same level as the air temperature before the start of the air heating system.
According to one of the conventional methods for raising the cooling water temperature after a long suspension of operation of a large-scale computer, the kinetic energy of vanes of water circulating pump in the cooling water system is connected into thermal energy which is applied to the water so as to heat the cooling water.
This type of technology is disclosed, for example, in an article "PACKAGING OF SUPER-COMPUTER SX SERIES FOR COOLING MULTI-CHIP PACKAGE" in the Nikkei Electronics, June 17, 1985, pp 243-266.
As described before, the most common method for controlling the cooling water temperature is to repeatedly start and stop the compressor of the refrigeration cooling system, and this method requires a large water tank so as to increase the quantity of the cooling water in the water cooling system in order to control the cooling water temperature in conformity with the command temperature. Such a water tank, however, requires a large installation space and, in addition, additional piping arrangement is necessary for connecting this tank, so that the size of the cooling system is undesirably increased. When the apparatus to be cooled by the system of the present invention is a large-scale computer which is in most cases installed in a computer room, a problem encountered is that the size of the casing of the cooling system including such a large water tank occupies a considerably large area in the limited space of the computer room, which is quite contrary to the demand for reduction in the installation area of the computer system.